In fabricating semiconductor devices, display devices, and the like, chemical vapor deposition (CVD) methods have been widely used to form thin films on substrates. CVD methods include plasma enhanced chemical vapor deposition (PECVD), thermal chemical vapor deposition, and the like. Plasma enhanced chemical vapor deposition (PECVD) forms films by decomposing and/or activating source gas in plasma. Thermal chemical vapor deposition forms films by heating substrates, thereby causing chemical reactions.
Another CVD method is “heating element CVD,” which forms films by decomposing and/or activating source gas using a heating element maintained at a high temperature. A heating element CVD apparatus includes a vacuum chamber into which a source gas is introduced, and a heating element comprising a metal having a high melting point, such as tungsten or the like, maintained at a high temperature of about 1,000° C. to about 2,000° C. After introduction, the source gas is decomposed or activated as it passes through the surface of the heating element. Then, the decomposed or activated source gas reaches a substrate, depositing a thin film on the surface of the substrate. Hot wire CVD, which uses a wire-shaped heating element, is one example of a heating element CVD method. Another heating element CVD method, in which the heating element undergoes a catalytic reaction to decompose or activate the source gas, is catalyst enhanced chemical vapor deposition (CECVD).
In CECVD, the source gas is decomposed or activated when it passes through the surface of the catalyst, thereby advantageously lowering the temperature of the substrate. In comparison, thermal chemical vapor deposition uses only the heat of the substrate to cause the chemical reaction. Further, unlike PECVD, CECVD uses no plasma, thereby preventing damage to the substrate due to the plasma. Thus, CECVD is expected to emerge as a method of film growth for next generation semiconductor devices, display devices, and the like having improved integration and performance, and fine pitch.
FIG. 1 is a schematic illustrating a CECVD apparatus according to the prior art. As shown in FIG. 1, the CECVD apparatus includes a chamber 1 having a side wall to which a vacuum pump (not shown) is connected through an exhaust pipe 2. The vacuum pump can exhaust the chamber 1, e.g., to a pressure of about 1×10−6 Pa. Further, the chamber 1 is connected to a gas supply pipe 3, which supplies reaction gas for growing thin films to the chamber 1. A substrate S for growing a poly silicon layer is loaded through a loadlock chamber onto a substrate support 4 inside the chamber 1. The substrate support 4 can be a graphite susceptor coated with SiC, and is heated by a heater 6 located outside the chamber 1. A catalyst wire 8 is located between a showerhead 7 at the end of the gas supply pipe 3 and the substrate support 4. A thermocouple 9 is attached to the substrate support 4 for measuring the temperature of the substrate S.
FIG. 2 is a cross sectional view of the CECVD apparatus illustrated in FIG. 1, including the catalyst wire, a catalyst support, the substrate support and the showerhead. As shown in FIG. 2, the CECVD apparatus according to the prior art includes a showerhead 7 which communicates with the gas supply pipe 3 and includes a plurality of injection holes 72 facing the inside of the chamber 1. The catalyst wire 8 adjoins the showerhead 7 and is supported by a catalyst support 84. Further, a gas line 82 supplies gas to the catalyst wire 8.
In such a CECVD apparatus, the catalyst wire 8 is adjacent to the shower head 7, and contaminants are not prevented from forming on parts of the catalyst wire 8 that function at low temperatures. Also, the gas line 82 for supplying gas to the catalyst wire 8 is provided in addition to the gas supply pipe 3 for supplying the reaction gas, thereby complicating the configuration of the showerhead 7. This construction makes it difficult to maintain the showerhead 7 and to supply the reaction gas uniformly in the chamber 1.
Further, this construction makes it very difficult to adjust the distance D between the showerhead 7 and the substrate S, the distance d1 between the showerhead 7 and the catalyst wire 8, and the distance d2 between the catalyst wire 8 and the substrate S. These distances, D, d1, d2, are important and are easily modified to adjust the introduction, decomposition, combination and exhaust of the reaction gas. Accordingly, to improve the reaction in the chamber, adjusting these distances is important.